Ceramic insulators are often used as electrical insulators in chemically and electrically hostile environments such as laser cavities. For example, the interior of a laser cavity typically contains several ceramic insulators. One such laser cavity is described in U.S. Pat. No. 4,959,840 to Akins et al., herein incorporated by reference in its entirety.
The ceramic insulators used in such cavities are typically formed from Al.sub.2 O.sub.3, but other ceramics may also be used. Typical rare gas halides that are used as lasing gasses in excimer lasers include XeCl, KrCl, ArF, KrF, and XeF. The ceramics used as insulators within excimer laser are often contaminated with impurities. For example, the common ceramic Al.sub.2 O.sub.3 is often contaminated with Si compounds (SiO.sub.2 specifically). This does not affect the insulating qualities of the insulator, and, therefore, the laser designers have heretofore not recognized such contamination as a problem.
Applicants have recognized that, during use of the laser, the Si present on the surface of the ceramic insulator reacts with components of the lasing gas. In fluorine lasing gasses used with Al.sub.2 O.sub.3 ceramics, SiF.sub.4 is formed because of the impurities in the ceramic insulator. The SiF.sub.4 absorbs a portions of the emission from the discharge area of the laser cavity, thereby causing the laser to be less efficient. The effects of this contamination are especially acute in ArF excimer lasers.
Others who have recognized this problem have attempted a solution that requires the application of a high purity ceramic insulator in the excimer laser. Japanese Pat. App. Publication No. 06-169119 and Japanese Pat. App. Publication No. 05-075182, for example, disclose this approach. However, a very high purity Al.sub.2 O.sub.3 ceramic is required in order to minimize the contamination by SiF.sub.4, which is a product of the SiO.sub.2 and F.sub.2 reaction. There is therefore a need for a solution which does not require the use such high-purity ceramic material, for economic and material availability reasons.